Automatic elevator conveyors have been commonly employed for various work processing machines. Such machines are known particularly for use in the electroplating workpieces. A plurality of carriers are mounted in a conveyor arrangement on an endless track with each carrier having a vertically movable work supporting arm, elevator locations for moving selected workpieces vertically and means for advancing the arms horizontally along a defined path of travel through work treating locations or stations such as plating baths. Typical of such machines is the apparatus disclosed in U.S. Pat. No. 2,826,288 and those sold by Hanson Van Winkle Muning division of Systems Engineering & Manufacturing Corp. of Stoughton, Mass.
Such elevator conveyors have carrier arms which normally move along the horizontal path and are retained from downward movement in a vertical direction by elevator guide rails and spaced flipper mechanisms.
Vertical indexing motion of the slide or carrier arms is typically caused by the simultaneous movement of two parallel chains, (an upper and lower chain) driven by a gear/shaft/driving force on one end, and a gear/shaft arrangement on the other.
A pair of guide channels for each slide arm are firmly affixed between the chains. The slide arm is mounted between the guide channels.
Up and down movement of slide arms with attached carrier arms is normally by means of an elevating mechanism. This mechanism has an elevator guide rail which rises from underneath a roller wheel on the back of each slide arm, thus lifting the slide arm as it rises. The lowering motion of the elevator normally allows the slide arms to descend by gravity. The elevator lowers to a point below which the slide arm motion ceases, allowing the arms to rest on a lower chain attachment.
In single station operation wherein the machine lifts, indexes forward, lowers, dwells and repeats the sequence, a fixed elevator guide rail is normally the only requirement. In multiple station processes, so utilized because a longer dwell or immersion time is required, the elevator guide rail must have movable devices, commonly known as flippers.
A "normally open" flipper is used at the entrance station of a multiple station tank. Its function is to be in the closed position when the elevator is up so it can receive a slide arm. Closed position is one in which its protruding rail or track is in the same plane as the fixed elevator guide rail so it can receive a slide arm as the chains index forward. After it receives said arm, it is lowered with the elevator. The lowering motion allows the arm to rest on the lower chain attachment. The elevator continues its lowering motion, disengaging the rail/slide arm relationship. The flipper now pivots to the "open" position, at an angle which allows it to safely pass the slide arm's engagement point when a lifting motion occurs. The arm is left in the down position, and will continue to index in the down position until another flipper, "normally closed" is used to re-engage the arm and return it to an up position.
In use, the slide arms are prevented from unwanted vertical drops by the underlying supporting flipper mechanism or fixed track. However, a problem has arisen in the positive positioning of the flipper mechanisms. When the slide arm reaches a predetermined work location in the up position, the flipper mechanism is supposed to be in a down position with a support plate supporting the arm normally in the plane of an upper guide rail. This position is imparted to the flipper plate (which is normally counterbalanced to an up opened pivoted position) by pins or mechanical stops of various kinds. It has been found in the past that such pins are sometimes ineffective to properly position the flipper plate due to misalignment in normal use, breakage or loss. When flipper plates are opened rather than in the down or safety position, when the slide arms reach their flipper positions, they will tend to drop abruptly. Such arms often carry substantial weights and volumes of workpieces which are then dropped into underlying tanks or stations. Aside from severe damage to the machine which can occur in these situations, a substantial safety hazard is presented to operators of the machine. Dangerous splattering of working solutions (which can be toxic acids) at the stations can occur, at a minimum, with severe damage to the work station or mechanism also often occurring.
A secondary but severe problem exists when the flipper does not open properly and partially engages the slide arm. The arm often falls with the same results as described above, or it will rise, be indexed forward and then fall because there is no fixed track provision between the entrance and exit positions of multiple station tanks.
Various electronic controls have been suggested for use in order to assure proper positioning of the flipper mechanisms. Such controls are costly and subject to unsure operations in certain situations. Known mechanical pin arrangements for assuring the position of the flipper plates while effective in most cases can become misaligned as described above.